Home agent optimization for handling mobile ip and static mpls (multiprotocol label switching)

ABSTRACT

For optimized IP-routing the invention discloses a home agent and method for transfer of an IP packet over a path from a sender (CN) over a radio access network (RAN, HA, FA  11 ) to a mobile host (MS 2 ), wherein, when a home agent (HA) receives an incoming data packet determined for a mobile host (MS 2 ) with a destination address (MS 2 -address  137.21.16.5 ), the home agent (HA) examines if there is a match between the destination address (MS 2 -address:  137.21.16.5 ) of the packet and a subnetwork address (FA  11 -address:  137.21.16.0 ) of a foreign agent (FA  11 ) stored in a list of subnetwork addresses ( 137.21.16.0; 137.22.25.0 ) stored in a list at the home agent (HA), wherein, if there is a match between the destination address (MS 2 -address:  137.21.16.5 ) and a subnetwork address (FA  11 -address:  137.21.16.0 ) of a foreign agent, the home agent examines whether a preconfigured path from the home agent (HA) to this foreign agent exists and wherein the home agent (HA) sends the packet to this foreign agent (FA  11 ) on this preconfigured label switched path ( 37 ) if a label switched path ( 37 ) to this foreign agent exists.

CLAIM FOR PRIORITY

This application is a national stage of PCT/EP2002/007860, published inthe German language on Jan. 22, 2004, which was filed in the englishlanguage on Jul. 15, 2002.

TECHNICAL FIELD OF THE INVENTION

The invention relates to a method and an optimized home agent fortransfer of IP datagrams over a path from a sender over a radio accessnetwork to a mobile host.

BACKGROUND OF THE INVENTION

The Mobile IP protocol is a concept to deal with user mobility issuesfor transport of IP related services. As a prerequisite the accessnetwork as well as the core network use IP as the network layer protocoland are capable to run, the mobile IP protocol in addition. The networkarchitecture for mobile IPv4 includes home agents and foreign agents tobuild forwarding IP tunnels, when a mobile host moves out of the homenetwork to attach to a different access point for requesting servicesfrom a network. The foreign agent represents the default router for amobile host, if it is attached to an access point outside the homenetwork. When a correspondent node sends packets to a mobile hostcurrently registered at a different location, the home agent interceptsall packets for that host and reroutes them to the new location. Thehome agent's binding cache contains rerouting information for all mobilehosts currently attached to different access points. The care-of-addressspecifies the mobile node's temporarily acquired host address afterregistering at a different location.

Using IP tunnels between home agent and foreign agent becomesinefficient, if the transport network already provides alternativetunneling mechanisms to interconnect various access points. The MPLScalled label switching approach offers support for IP trafficengineering by introduction of virtual circuit switched services inconnectionless IP based networks. Other benefits of MPLS include theestablishment of virtual private networks and provision of traffictrunks with dedicated reserved bandwidth between two endpoints of a path(tunnel). When label switching is active, packet forwarding is based ona fixed label instead of an IP network address or prefix in the routingtable. A label is attached by a label ingress router, which is theingress router of the MPLS path. The label egress router represents theendpoint of a MPLS tunnel. Path setup requires a signaling protocol toagree on path attributes like labels to be used and requested bandwidthfor the path etc. Examples are CR-LDP, RSVP-TE or BGP enhancements.

A network operator has to deal with convergence issues, if there is astrategy to offer mobile IP based services in a network, which has beenengineered for MPLS. Functional components for mobile IP and MPLS mayreside on the same network node in the situation described above. Forexample one network node may include home agent and label edge routerfunctionality at the same time. The same applies to the mobile foreignagent. It is the challenge of equipment manufacturers to provideintegrated solutions for network components, in a way that mobilehome/foreign agent are optimized for interworking with MPLS. It meansthat existing MPLS tunnels may be used for rerouting purposes in mobileIP instead of establishing a separate IP tunnel in parallel. This wouldallow the network operator to easily adapt mobility services to a MPLSinfrastructure without the need for complex network resource management.There is no need to manage MPLS and IP tunnels in parallel.

Mobile IP and MPLS are emerging technologies. Though definition ofconcepts is quite stable there is no widespread usage so far. A simpleapproach is to deploy both technologies independently of each other andneglecting the possibilities of convergence. Thus MPLS paths would notbe used to transport redirected packets to a mobile foreign agent.Instead MPLS tunnels for traffic engineering purposes and IP tunnels formobile IP support would exist in parallel. However such a heterogeneousnetwork would enlarge the effort for management of tunnels and representa burden for consistent network engineering due to differenttechnologies to be deployed in parallel.

A different approach is a loose coupling between MPLS and mobile IP.Home agent and label edge router would reside on the same network nodewithout direct interaction between these components. The same applies tothe foreign agent, which includes the label edge router functionalcomponents as well. Packets, which are destined for a mobile host, whichis attached to a foreign access point would have to be transported bymeans of an IP tunnel and a MPLS tunnel as well for the loose coupling.Home agent in this example first would have to encapsulate the native IPpacket with an additional IP header, afterwards a label is attached tothis packet by the label switching ingress router. As a benefit a pureMPLS network might be sufficient to forward packets to the foreign agentfor the loose coupling approach. Nevertheless advantage of labelswitched paths is not used completely, since an additional IP tunnel isrequired.

SUMMARY OF THE INVENTION

The invention is an efficient transport of mobile IP traffic. Theinvention described herein provides optimal usage of an existing staticMPLS infrastructure while introducing IP mobility services. Static heremeans that label switched paths have been configured in advance based onmechanisms like traffic engineering. Primarily the focus is on a singleadministrative domain, where a network operator controls network nodes,which are involved in mobility issues. Though the mechanism is notrestricted to a single network domain. With the invention, fulladvantage of an existing MPLS network can be gained for mobile IPforwarding. It is assumed that by means of traffic engineering a mesh oflabel switched paths has been established, which can be used forredirecting packets between any pair of mobile home agents and foreignagents in the current administrative domain. For the purpose of mobileIP no additional label switched paths have to be created or modified. Aswell no IP tunnels are required between a home agent and a foreignagent. The solution for convergence proposes an optimisation of mobilehome/foreign agents by efficiently incorporating label edge routerfunctionality. A tight coupling between MPLS and mobile IP is achieved.No changes for existing protocols like mobile IP or label distributionprotocol are required. Efficient usage of preestablished label switchedpaths for the transport of redirected packets between mobility agentsrequires traffic engineering for mobility. In that context it isnecessary to gain knowledge about behaviour of mobile users, i.efrequency of leaving home networks, services to be requested at foreignaccess points etc.

The mechanism described for convergence between MPLS and mobile IP maybe extended to different administrative domains. Macro mobilitydescribes the situation, where a mobile user might attach to an accesspoint, which is controlled by a different administrative authority in ageographically distinct area. Mobile IP forwarding and MPLS pathsbetween separate domains may be enabled if service level agreements areestablished between adjacent network domains.

Advantageous features of the invention are:

-   A modified home agent, which includes label edge router capability.    Packet forwarding to any mobile host in a visited network is done    exclusively by means of label switched paths, which interconnect    mobility home and foreign agents. Thus for new mobility bindings in    the home agent no creation or modification of label switched paths    is required.-   An extended algorithm for mobility forwarding in home agent: If the    mobile binding cache contains an entry, which corresponds to the    destination address of an incoming packet, the home agent tries to    map this care-of-address of the mobile node to a subnetwork address    of the list of potential visited subnetworks. After the correct    visited subnetwork has been identified the home agent is responsible    to determine the proper label switched path for packet forwarding.    Each subnetwork is associated with a label and the correct egress    interface to use at the home agent.-   Usage of multipurpose label switched paths: These paths are not    dedicated for mobile IP and therefore may transport packets for any    other purpose as well.-   A list of potential visited subnetworks in the operators network    domain. This list is maintained by-each home agent in the network    domain and configured by means of network administration principles.    The list is required to enable mapping of the mobile nodes care of    addresses to a visited subnetwork.-   An aggregated FTN table (Forwarding equivalence class To Next hop    label forwarding entry): Generally for MPLS label switching the    ingress router maintains this table for determining the necessary    label and interface to use for a specific destination address. The    home agent maintains this table with a single entry for each    potential visited subnetwork, instead of an individual entry for    each mobility binding. Thus mobile hosts attached to the same    visited subnetwork correspond to one and the same entry in FTN    table, which introduces scalability for the combined MPLS/mobility    approach.-   A network with preconfigured statically administrated label switched    paths. No paths have to be created or modified for the purpose of    mobility handover. As a consequence signaling load in the network is    reduced and handover delay is independent of setup time for label    switched paths. These paths should provide enough bandwidth capacity    to enable successful handover of mobile users almost anytime. Thus    traffic engineering becomes a major issue for mobile IP with    statically managed label switched paths.-   A foreign agent, where the functional entities of mobile IP and MPLS    are co-located, but not correlated. Thus the label egress router    component runs in parallel on the same host.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the invention are apparent from the followingdescription of an example of the invention illustrated in FIG. 1.

FIG. 1 shows a block diagram of an IP network.

DETAILED DESCRIPTION OF THE INVENTION

Three mobile stations MS 1, 2, 3 use some wireless link layer technologyto connect to an IP based radio access network 4. Correspondent basestations BS 5, 6, 7 terminate the radio interface. The radio accessnetwork provides mobility support and uses label switched paths LSP 37,62 for internal transport as already described for this invention.

Connectivity to transport networks 14 is achieved via border routers BR8, 9, which separate the administrative domains. In this example allthree mobile stations 1, 2, 3 are located in the same home network4—they get access by the same edge router, which includes the home agent(15) functional component at the same time. MS 2 and MS 3 currentlymoved to different access points (BS 6,7) and attach to the networkthrough foreign agents FA 11 and FA 12 respectively. Two. LSP's 37, 62are illustrated for label switching between home agent HA 15 and foreignagents FA 11, 12. A correspondent node CN 13 typically located at anyaccess point beyond the local network 4 should send data to three mobilestations 1, 2, 3. For packets destined for MS 1 no entry in the bindingcache (in 15) is available, thus packets are directly forwarded to MS 1.Now CN 13 sends data to MS 2. Home agent HA 15 includes a binding for MS2 with care-of-address 137.21.16.5. From a configured subsystem list,the home agent is aware that MS 2 is currently reachable throughsubnetwork 137.21.16.0. Finally correspondent entry in FTN table forthat subnetwork indicates that home agent needs to code “label 37” onits interface eth0 to forward the packet to the proper label switchedpath 37. Since LSPs are unidirectional they have to be originated at theHA and terminated at the FA. The illustration includes a further examplefor MS 3, which is attached to a different access point BS 7, where yetanother label switched path (LSP 62) is used to forward packets to thecorrect destination (via FA12, BS7 to MS 3).

1. A method for transfer of an IP packet over a path from a sender overa radio access network to a mobile host, comprising: examining, when ahome agent receives an incoming data packet determined for a mobile hostwith a destination address, if there is a match between the destinationaddress of the packet and a subnetwork address of a foreign agent listedin a list of subnetwork addresses stored at the home agent (HA); andexamining, if there is a match between the destination address and asubnetwork address of a foreign agent, whether a preconfigured path fromthe home agent to the foreign agent exists and sending the packet to theforeign agent on the preconfigured label switched path if a labelswitched path to the foreign agent exists.
 2. The method according toclaim 1, wherein the home agent sends the packet to the foreign agent onthe preconfigured label switched path by sending the packet over a portof a forwarding interface of the home agent which port is used for thepath with the path number.
 3. The method according to claim 1, whereinthe home agent examines if there is a match between the destinationaddress of the packet and a subnetwork address of a foreign agent ifthere is an entry in a binding cache of the home agent which entrycorresponds to the destination address of the incoming packet.
 4. Themethod according to claim 1, wherein a handover of a mobile host fromone foreign agent to an other foreign agent is done without creating ormodifying a path between the foreign agent and a home agent of themobile host.
 5. The method according to claim 1, wherein the path is apreconfigured, statically administered, multipurpose label switchedpath.
 6. The method according to claim 1, wherein the functionalentities of mobile IP and multipurpose label switching MPLS areco-located but not correlated in a foreign agent.
 7. The methodaccording to claim 1, wherein a foreign agent and a home agent arepacket switched nodes of an IP network.
 8. A home agent, comprising: amemory including a list of subnetwork addresses of foreign agents; acomparing device for comparing the destination address of an incomingdata packet determined for a mobile host with stored subnetworkaddresses of foreign agents for determining the foreign agent to whichthe packet is to be sent; a device for determining a path fortransmission of the packet to the foreign agent by comparing thedetermined foreign agent address with stored addresses of foreignagents, between which foreign agents and the home agent paths exist; andan interface for transmitting a packet to a determined foreign agent ona determined, preconfigured path.